electrical subpanel question

[brackishdude]

Thanks, everyone.

There are instances when the neutral and ground can be bonded at the sub panel. In those cases, NO OTHER metal or material capable of carrying current can connect the two buildings. THE PANELS MUST NOT BE IN THE SAME BUILDING.

Yes, the pumphouse is a separate building and is fed via underground metal pipe, two hots and a neutral (no formal ground). Unknown if the pipe is in continuity with the house main ground. How would I test?


If the pipe/conduit is not tied into the main house ground, you're saying the shared neutral/ground bus in the subpanel is ok, but that I have to ground it too?

And if the pipe is in contiuity with main hous ground, then the shared bus is not OK, and I need to add a dedicated ground bus which will ground through the subpanel housing and thus the incoming pipe?

If so, then I hope the pipe is not in continuity with the main house, because then all I have to do is gound the box, versus putting in a new bus and rewiring. . .

 

[BeanAnimal]

<a href=showthread.php?s=&postid=9544388#post9544388 target=_blank>Originally posted</a> by brackishdude
Thanks, everyone.




Yes, the pumphouse is a separate building and is fed via underground metal pipe, two hots and a neutral (no formal ground). Unknown if the pipe is in continuity with the house main ground. How would I test?

By attaching a multimeter (set on ohms) between the ground in the house to the pipe in the pool house. However, that does not get you out of the woods one way or the other. Also note that telephone wires, plumbing (gas or water) and many other items can be considered conductors between the house and the outbuilding. The area can get kind of grey.. but I would imagine you poolhouse has a spigot and it is from the same metered supply as your house.

If the pipe/conduit is not tied into the main house ground, you're saying the shared neutral/ground bus in the subpanel is ok, but that I have to ground it too?

The metal conduit is one aspect. You still have to meet the other provisions of the code. I would contact a pro and get their opinion. I simply can not give you that kind of advice. My advice would be to pull in a ground and isolate the neutral bus (if the conduit has enough room).

And if the pipe is in contiuity with main hous ground, then the shared bus is not OK, and I need to add a dedicated ground bus which will ground through the subpanel housing and thus the incoming pipe?

Well that depends on the classification of that conduit. But the easy answer is still NO, YOU SHOULD ISOLATE THE NEUTRAL. Now if the conduit is bonded and rated and installed as such, then it could take the place of the grounding conductor.

Again, please note that MANY local codes go one step further than the NEC. They totaly phrohibit 3 wire feeders and neutral bonded sub panels. Many local codes also prohibit the use of the conduit as the EGC (Equipment Grounding Conductor). No matter how you roll the dice, you come up with one good answer. That is isolate neutral from ground in a subpanel.

If so, then I hope the pipe is not in continuity with the main house, because then all I have to do is gound the box, versus putting in a new bus and rewiring. . .

Sometimes the easy way is not the safest way. Seeing that WATER is also involved here, you may want to take the high road and pull in the ground conductor.